London, Nov. 2: The more fertile a woman, the more attractive she is to men, scientists claimed today.

For many years, scientists believed that when lovers gaze at each other they are merely using facial clues ' large eyes, small nose, large lips and so on ' to check that their prospective mate has high “fitness” and can efficiently pass their genes to the next generation.

The female sex hormone oestrogen was thought to be the mediator of beauty, which advertises health and fecundity. Now researchers at the University of St. Andrews have shown for the first time that women with higher levels of oestrogen do indeed have more attractive faces.

The study, published today in the Proceedings of the Royal Society: Biological Sciences is the first to demonstrate that women’s facial appearance is linked to their well-being because oestrogen impacts on women’s reproductive health and fertility.

“People have speculated for years that women with more attractive and healthy looking faces have higher oestrogen,” said Miriam Law Smith.

Hormones exert most effect on the face during puberty, she said. The principal male sex hormone testosterone cause the jaw and eyebrow ridges to be more prominent and facial hair to grow, making boys’ faces grow more than girls’.

Oestrogen prevents the growth of facial bone, reduces the size of the nose and chin, and leads to large eyes, increased thickness of lips and fat deposition in the cheek area, along with hips and buttocks, features that announce that a woman is fertile.

At first sight, the discovery that beauty is more than skin deep suggests that oestrogen injections could boost the attractiveness of a developing female face.

However, the way the body would react to an artificial boost is unknown and there would be a downside, as underlined by the risks of hormone replacement therapy. Moreover, today’s study shows the effects of hormones are easily masked by the application of make-up.

Because the shape of the face is determined during puberty, boosting oestrogen in later life may improve the appearance of the skin but would not change the face, added Law Smith.

The team photographed 59 women’s faces aged between 18 and 25 and analysed their sex hormone levels. Women with higher levels of oestrogen were rated as more attractive, healthy and feminine looking. Interestingly, no relationship between appearance and oestrogen was found in women wearing make-up.

The researchers believe that while make-up improves facial appearance it may be masking cues normally seen in the face. “Women are effectively advertising their general fertility with their faces. Our findings could explain why men universally seem to prefer feminine women’s faces. In evolutionary terms, it makes sense for men to favour feminine fertile women, those that did would have had more babies,” Law Smith said.

Earlier this year, evidence that very early exposure to sex hormones appears to form a basic facial shape was reported. The relative length of the index to ring finger ' which is linked to exposure to prenatal sex hormones ' was found to be associated with face shape by the team in an analysis of more than 100 people.

Exposure to early testosterone, as indicated by finger length patterns, causes male and female faces to look rugged with wide jaws and strong cheekbones whereas exposure to high oestrogen levels makes them appear less robust. This may be because prenatal hormones correlate with levels found at puberty.